The present invention relates generally to seals. More particularly, the invention relates to fluid seals disposed around a moving shaft.
Seals are generally known for preventing fluid leakage around a shaft which is rotating or reciprocating. A particular example is a water turbine which has an annular seal disposed around a rotating shaft. Water turbines are used in dams for powering electric generators. Such a turbine can be quite sizeable, and can have a massive shaft that is several feet in diameter.
Many turbines have variable pitch vanes. A mechanism for rotating the vanes is housed inside the shaft. This mechanism requires lubrication. Furthermore, the shaft rides on bearings which must also be lubricated. In order to lubricate these components, it is desirable to provide a lubricant around a portion of the shaft. However, it is undesirable for the lubricant to mix with water around the shaft near the vanes.
Therefore, it is necessary to provide a seal around a rotating turbine shaft to prevent water flow around the shaft from a vane portion of the turbine. It is also necessary to provide a seal to prevent the flow of lubricant from a lubricated portion of the shaft.
Because of the great size and mass of water turbine components, it has been a problem to replace worn seals around a shaft. Disassembling turbine components is difficult and time consuming. Furthermore, it is highly inefficient to remove a turbine shaft only to replace an annular seal.
As an attempted solution, it has been known to provide a "split" seal. Such a seal has a split, or separation so that the seal is not a continuous annular piece, but rather has ends that must be connected by some means, such as with an adhesive. Use of such a seal allows replacement around a shaft without major disassembly of surrounding equipment.
Unfortunately, traditional split seals often fail at the split portion. Such a failure can result in a small leakage or a complete breakage altogether. Therefore, a need exists for a split seal that has a strong connection at the split.
Furthermore, water turbine shaft seals, if disposed on a horizontal axis, have a tendency to wear at the bottom. Because of the great weight and forces within a water turbine, present bearing assemblies are incapable of completely preventing this effect. Therefore, a need exists for a seal which can be repaired in only a worn section.
Seals referred to as "lip" seals are generally known in the art. Such seals have an annular channel in the side thereof. Formed around the channel is an inner lip and an annular boss. The channel is configured to be open to pressurized fluid. This pressure on the interior of the channel forces the inner part of the seal inward and the outer part of the seal outward, enhancing the sealing effect.
A lip seal can be one-sided or two-sided. A one-sided lip seal has an annular channel on one side; a two-sided lip seal has an annular channel on each side.
Also, it is known to provide a rigid backing ring behind a one-sided lip seal to retain a seal's shape or for securing a seal in position.